With energy resources, however, factors other than supply and demand also come into play, and some, such as the indirect costs resulting from atmospheric pollution, are tricky to deal with. Some indirect costs of burning fossil fuels are included in the price we pay for energy. The cost to an electric utility or manufacturer for reducing the emissions from a factory or power plant is included in the price we pay for electricity and consumer goods. The cost to a coal company of restoring strip mines and making the land productive once again is passed on in the price paid for coal. But what of the costs that are not included in the price we pay? What of the costs for instance of health problems such as asthma, emphysema, and heart disease that are aggravated by smog and ozone produced by cars, trucks, and planes? What of the cost of environmental damage from oil spills and acid rain? What of the more easily understood costs of highway maintenance and repair?

Well, most of us don't associate the various costs for energy bills. We pay for them nonetheless. Some are hidden in today's costs for health care, farm products, and manufactured goods. Some we pay for in fuel taxes. Other costs, however, will not come due for years or even decades. The most important of these may be the economic consequences of climatic change resulting from the buildup of greenhouse gases in the atmosphere.

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Carbon dioxide in the atmosphere absorbs heat that is radiated from the Earth. Instead of moving out into space, much of this heat is radiated back to the surface. This process has moderated Earth's temperature for hundreds of millions of years, making it habitable. But if the amount of carbon dioxide in the atmosphere increases dramatically, this delicate equilibrium could shift, and global temperature might begin to rise significantly.

Our present understanding of atmospheric change and global warming is by no means complete. Nevertheless, records contained in ice up to two hundred and fifty thousand years old from the Greenland ice sheet does show that carbon dioxide has been accumulating in the atmosphere at an extraordinary rate for the past century.

If this rate of increase continues, many scientists believe that it will lead to significant global warming. Such change could cause a shift of major agricultural belts that might turn existing farmland into deserts. Melting of polar ice caps might flood coastal cities and displace large populations. These potential dangers and the indirect costs that result from energy use suggest that we should at least bring clear and careful consideration to our energy choices.

Burning natural gas compared with other fossil fuels does add smaller amounts of carbon dioxide and other compounds to the atmosphere. A methane-fueled car emits about twenty-five percent less carbon dioxide, forty percent less nitrogen oxides, forty-five percent less of the compounds that create smog, and eighty-five percent less carbon monoxide compared to an average gasoline-fueled vehicle.

In electrical power generation a natural-gas-fueled combined cycle plant will emit fifty percent less carbon dioxide, ninety-five percent less nitrogen oxides, and one hundred percent less sulfur oxides than a scrubbed coalfield plant. These comparisons indicate that increased use of natural gas would let us begin the process of reducing the amount of carbon dioxide and other pollutants added to the atmosphere.

But the utilization of natural gas does have other consequences. When leaked into the atmosphere, methane contributesd significantly to the greenhouse effect and might intensify global warming. Evidence indicates that the amount of methane in the atmosphere has doubled during the past one hundred and fifty years of population growth and economic development. This is a little deceptive, however, as atmospheric methane comes from a variety of sources. Gas seeps and wetlands account for about one-third of the methane presently added to the atmosphere. This is the natural and continuing flow of methane from the Earth that has been taking place for millions of years.

The two-thirds that's increasing comes from human activities. Agriculture, particularly rice cultivation and cattle raising, produces one-half of this. The final third comes from oil and natural gas activities, coal mines, landfills, and the breakdown of debris from clearing forests.

As energy use increases worldwide, potential leakage during transportation of liquefied natural gas by tanker from gas fields in Russia, Algeria, Nigeria, and Venezuela will become an additional source of atmospheric methane. If use of natural gas is to help reduce the potential danger of atmospheric change and global warming, leakage from all sources worldwide will have to be kept to a small percentage of the total amount used.

Measures to limit methane generated by human activities are underway. Natural gas distribution and transmission lines are being improved. Coalbed methane is being captured for use as a fuel, and methane extracted from landfills is being added to city fuel supplies or used to generate electricity.

Natural gas also comes with a land use price tag. Presently our supplies come from some two hundred and forty thousand wells. At least twenty thousand wells will need to be drilled each year to maintain present production. Even more may be needed if we are to fully utilize the thirteen hundred trillion cubic feet that is now available. While natural gas wells can be very unobtrusive, networks of access roads cut across the land.

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To really improve the condition of the atmosphere, even natural gas would need to be replaced in a few decades by a cleaner energy mix. This might include increased use of renewable resources and even nuclear fusion.

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Or it might mean using hydrogen which powers this experimental car. Hydrogen, however, does not occur naturally in large quantities and would have to be produced from water or even methane using energy from renewable resources.

Some experts think that new, clean-burning coal technologies will fuel society for centuries, but no matter what fuel we decide to use, most energy analysts agree that increased efficiency and conservation must play a more significant role in energy planning.